Synchrotron (circular particle accelerator)

How it works

Particles are injected into the ring and pass repeatedly through radio-frequency cavities that provide short bursts of accelerating electric field. Magnets around the ring bend and focus the beam: dipole magnets provide the main bending force, quadrupoles focus the beam transversely, and higher-order magnets correct subtle deviations. As the particles gain energy, the magnetic field strength is increased in step so the trajectory radius stays essentially constant — a condition called synchronism.

Key components

• RF cavities: supply the accelerating electric fields timed to the particle bunches.
• Bending magnets (dipoles): force the beam into the circular orbit and determine its curvature.
• Focusing magnets (quadrupoles and sextupoles): keep the beam compact and correct optical errors.
• Injection and extraction systems: add particles to the ring or remove them for experiments or transfer to other machines.

History and development

The principle of synchronizing accelerating and guiding fields — sometimes called phase stability — was developed in the mid-20th century and led to the first practical synchrotrons. Several physicists contributed to the concept and early construction of machines: theoretical proposals and prototype electron and proton rings were built in the years following World War II. These early developments established the synchrotron as a route to energies not easily reached by linear or fixed-field cyclotron designs.

Applications and importance

There are two broad roles for synchrotrons. In particle physics, large synchrotrons accelerate protons, electrons or ions for collision experiments that probe fundamental particles and forces. In materials and life sciences, so-called synchrotron light sources use the intense X-rays emitted when electrons are bent by magnets; those X-rays enable high-resolution imaging, spectroscopy, and studies of chemical and biological structures. Synchrotron facilities support research in chemistry, geology, medicine and industrial development.

Notable distinctions and facts

Synchrotrons are distinct from storage rings and cyclotrons by their method of synchronizing fields and their adaptability for very high energies. A related phenomenon, synchrotron radiation, is both a challenge and an asset: it causes energy loss in high-energy accelerators but also provides extremely bright, tunable photon beams for experiments. For further background on accelerator types and technologies see accelerator overview, material on magnetic systems at magnet design, and resources about RF acceleration at RF cavities and timing.